The present invention relates generally to shrink films, and more particularly to shrink films having an internal layer of high density polyethylene.
Various films and laminates are available for shrink packaging applications. These films and laminates (hereinafter collectively "films") ideally possess several properties which make them useful in packaging food and non-food items.
One particular property that is often desirable in shrink films is low moisture permeability. The inventor has found that a film with good shrink properties, heat sealability, and low moisture permeability includes an internal layer of high density polyethylene, and outer layers of ethylene polymers or copolymers.
Of interest is U.S. Pat. No. 4,355,076 issued to Gash wherein a monoaxially oriented polypropylene film may be laminated to a monoaxially oriented high density polyethylene film, said films produced by e.g. tubular blowing.
Also of interest is U.S. Pat. No. 4,188,443 issued to Mueller et al disclosing a five-layer film having two inner layers comprising ethylene vinyl acetate copolymer, and skin or outer layers comprising an ethylene propylene copolymer.
U.S. Pat. No. 4,258,156 (Canterino et al) discloses a uniaxially oriented plastic film made of low density polyethylene, or copolymers of ethylene with other unsaturated monomers, such as vinyl acetates, or olefinic monomers made by low pressure polymerization techniques.
U.S. Pat. No. 3,817,821 (Gallini) discloses a film with a core layer of HDPE, and surface layers of polyethylene and EVA.
U.S. Pat. No. 4,380,567 (Shigemoto) discloses a film with a layer of high density polyethylene and layers of an ethylene alpha olefin copolymer.
U.S. Pat. No. 4,724,185 (Shah) discloses an oriented film with outer layers of a blend of linear low density polyethylene, linear medium density polyethylene, and ethylene vinyl acetate copolymer.
U.S. Pat. No. 4,82B,928 (Shah) discloses a monoaxial shrink film with a core layer of high density polyethylene, outer layers of ethylene propylene copolymer and/or polypropylene, and intermediate bonding layers.
An article, New Biax Film Technology, appearing in Plastics Technology, June 1989, page 45, discusses a biax HDPE film with a surface crosslinked with electron radiation, and better moisture barrier than OPP.
It is an object of the present invention to provide a thermoplastic film with good shrink properties and low moisture permeability.